<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>

	<style>
		button{
			width: 50px;
			height: 50px;
		}
	</style>

</head>
<body>
	<button id="bt">点我</button>
	<button id="bto">碰我</button>
	<div id="a">111</div>
		
	<script>
		var abt=document.getElementById('bt');
		var bbt=document.getElementById('bto');
		var aaa=document.getElementById('a');

		abt.onclick=function(){
			aaa.style.color="red";
		}

		bbt.onmouseenter=function(){
			aaa.style.color="lime";
		}

		bbt.onmouseleave=function(){
			aaa.style.color="orange";
		}

	</script>
</body>
</html>